Oviposition site selection and attachment ability of Propylea quatuordecimpunctata and Harmonia axyridis from the egg to the adult stage

Surface features of plants can influence the searching efficiency and survival of predatory insects. Surfaces act as barriers preventing attachment of both phytophages and also their insect predators. In this regard, we focused on the oviposition site selection and the attachment ability of all life stages (eggs, larvae, imagines) of two common ladybird species, Propylea quatuordecimpunctata and Harmonia axyridis (Coleoptera: Coccinellidae), on artificial and natural substrates with different surface features and properties (roughness, wettability). Both species preferred a hydrophilic surface as the oviposition site and this can be correlated with the better performance of both larvae and adults on these substrates compared with hydrophobic ones. The egg glue of both ladybird species can wet hydrophobic surfaces such as those of many plant leaves and also with prominent 3D wax coverage. The surface roughness has an important role in the oviposition site selection in P. quatuordecimpunctata, but not in H. axyridis. The oviposition preference for smooth surfaces in P. quatuordecimpunctata could be due to better performance of larvae on smooth substrates compared with rough ones. The egg glue of both species can adapt to artificial and natural surfaces characterized by different asperity sizes faithfully replicating their shape, except for very high asperity sizes or big trichomes. The results of the present research can shed light on the mechanical ecology of the evolutionary successful Coccinellidae and may aid in the development of suitable substrates for coccinellid egg-laying, in order to improve the mass rearing technique of species used in biological control.